1. Technical Field
The present invention relates to a disk drive provided with a disk recording medium having a sector servo format, and in particular to a servo information detection timing controlling method for controlling the timing of servo information detection in a signal read from the disk recording medium in the disk drive. The invention further relates to a disk rotational speed controlling method for controlling the rotational speed of the disk recording medium in the disk drive, and more particularly to a servo information detection timing controlling method and a disk rotational speed controlling method that can detect servo information stably and surely even when the disk is shifted from a rotation center of the disk recording medium.
2. Description of the Related Art
Occasionally, as shown in FIG. 4, a center C of servo information writing (i.e., center of a track) is shifted from a center 0 of the disk rotation (i.e., center of the spindle rotation) in a disk drive provided with a disk recording medium having a sector servo format, and the radius from the center 0 of the disk rotation in a servo sector in the same track is changed.
In order to compensate such a radius change in a servo sector that occurs due to disk shifting as described above, there is disclosed a technique that enables servo controlling with use of a peak filter that employs, for example, the same frequency as that of the disk rotational speed (rpm) as its peak frequency.
FIG. 14 is a flowchart of a conventional servo system controlling procedure that compensates disk shifting with use of such a peak filter. Steps S1 to S5 and S8 to S15 in FIG. 14 are identical to those with the same numbers in FIG. 9 in the first embodiment of the present invention to be described later. The steps S1 to S3 and S10 to S15 will be described with reference to FIG. 9.
At first, in step S4, a search window is set for a signal read by a head from a disk so as to search a servo address mark (SAM) for recognizing a servo area. The SAM is recorded in the servo area.
In case the SAM is detected in step S4, thereby the servo area state is decided as a servo lock and the head is not changed in step S5, the initial value TS0 of a time interval between servo sectors is set in step S41. Consequently, the search window is set for each time interval TS0.
Then, in step S8, servo information is sampled from the signal read from the servo area and according to this servo information, a VCM control current value CNT is calculated. In addition, a VCM control current value CNTF obtained by filtering the VCM control current value CNT with use of the above peak filter is calculated. This VCM control current value CNTF is then supplied to the VCM driver.
After that, in step S9, the above VCM control current value CNTF is used to calculate an internal variable value of the peak filter. Control then goes back to step S4.
Because the above VCM control current value CNTF includes a displacement xcex94r component of the servo sector in the radial direction of the disk, which is caused by disk shifting, the head position is compensated according to the radius change of the servo sector from the center O of the disk rotation.
However, the above conventional method may not detect a servo address mark SAM, since the SAM does not come into the search window in the worst case. This is because a search window is set at a fixed time interval, whereby disk shifting causes the radius of a servo sector from the center of the disk rotation and the time interval between servo sectors to be changed thereby causing a margin for detecting servo information surely and stably to be reduced. Consequently, in some cases, the conventional method may detect user data as a SAM by mistake.
Under such circumstances, the present invention recognizes that a need exists o provide a servo information detection timing controlling method and a disk rotational speed controlling method that can detect servo information surely and stably even when a time interval between servo sectors is changed due to disk shifting.
In order to achieve the above object, a servo information detection timing controlling method of the present invention comprises (1) calculating a time interval TS(i) between passing of a servo sector in a servo area SF(i) under the read/write head and passing of a servo sector in a next servo area SF(i+1) under the read/write head according to a displacement xcex94r(i) of the servo area SF(i) calculated with use of already detected servo information in the radial direction of the disk, and (2) adjusting a time interval for detecting servo information according to the time interval TS(i).
In another embodiment, the invention provides a disk rotational speed controlling method comprising (1) calculating a compensation value for the rotational speed of the disk recording medium for keeping at a predetermined value the time interval between passing of a servo sector in a servo area SF(i) under the read/write head and passing of a servo sector in the next servo area SF(i+1) under the read/write head according to the displacement xcex94r(i) of the servo area SF(i) calculated with use of already detected servo information in the radial direction of the disk, and (2) adjusting the rotational speed of the disk recording medium according to the compensation value.